The compound 2,6-bis-(diethanolamino)-4-piperidinopyrimido[5,4-d]pyrimidine, known as mopidamol, is disclosed in U.S. Pat. No. 3,031,450, incorporated herein by reference. This compound has been successfully used as an active substance, such as an antimetastic agent, for many years. The pharmaceutical preparations previously known which contain this active substance have a number of disadvantages for certain applications due to the special physical properties of mopidamol.
Mopidamol is readily water-soluble only in an acidic medium, and therefore it can only go into solution from solid pharmaceutical forms and then be absorbed if the pharmaceutical preparations remain in the acidic range for a sufficiently long period. Thus, the solubility and hence also the absorption greatly depend upon the retention time and the pH in the stomach and upper intestinal tract. This results in sharp inter-individual and intra-individual fluctuations in the blood levels since the motility of a patient, the pH of the patient's stomach and intestines, and the patient's food intake have a considerably influence on absorption. In some patients the blood levels may even be so low that they practically amount to an absence of absorption.
The problems concerning administration of mopidamol are similar to those of a related compound, dipyridamole. Improved delivery pharmaceutical forms for dipyridamole are described in co-pending, U.S. patent application Ser. No. 389,282, filed June 17, 1982, now U.S. Pat. No. 4,427,638, incorporated herein by reference.